Robust Arctic sea-ice influence on the frequent Eurasian cold winters in past decades

Abstract

Over the past decade, severe winters occurred frequently in mid-latitude Eurasia 1,2 , despite increasing global-and annual-mean surface air temperatures 3 . Observations suggest that these cold Eurasian winters could have been instigated by Arctic sea-ice decline 2,4 , through excitation of circulation anomalies similar to the Arctic Oscillation 5 . In climate simulations, however, a robust atmospheric response to sea-ice decline has not been found, perhaps owing to energetic internal fluctuations in the atmospheric circulation 6 . Here we use a 100-member ensemble of simulations with an atmospheric general circulation model driven by observation-based sea-ice concentration anomalies to show that as a result of sea-ice reduction in the Barents-Kara Sea, the probability of severe winters has more than doubled in central Eurasia. In our simulations, the atmospheric response to sea-ice decline is approximately independent of the Arctic Oscillation. Both reanalysis data and our simulations suggest that sea-ice decline leads to more frequent Eurasian blocking situations, which in turn favour cold-air advection to Eurasia and hence severe winters. Based on a further analysis of simulations from 22 climate models we conclude that the sea-ice-driven cold winters are unlikely to dominate in a warming future climate, although uncertainty remains, due in part to an insu cient ensemble size.The Siberian High, a continental surface high pressure prevailing the boreal winter Asian monsoon, causes a breakout of cold air to the mid-latitudes, the fluctuation of which greatly affects a significant part of the population of Eurasia. Northern Hemisphere winters (December-February; DJF) have frequently seen pronounced warming and cooling in recent years, in the Arctic and mid-latitudes, respectively, forming the so-called 'warm Arctic-cold continents' pattern 7 (Supplementary Fig. 1), signifying the intensification of the Siberian High over the Eurasian continent. The Arctic surface warming has been accompanied by a rapid decline of Arctic sea ice 8 , which is therefore argued to represent the Arctic amplification signature of global warming 9,10 . However, the causes of these cold winters observed over mid-latitude Eurasia, apparently counteracting the continuous rise of annual-mean surface air temperature (SAT) over land 3 , are not well understood.Observational studies show a statistically significant relationship between cold SAT anomalies over Eurasia and Arctic sea-ice decline 2,4,11,12 , suggesting that the latter forces the former. However, a robust atmospheric response to sea-ice loss has yet to be obtained by modelling studies 2,13-16 because detection of sea-ice loss impacts on the extratropical atmosphere is hampered by the large internal fluctuations of the atmospheric circulation that are prominent in winter 6,15 .Here, we successfully detected the signature of Eurasian cold winters excited by sea-ice decline in the Barents-Kara Sea (BKS), where a pronounced change has been observed during winters since 2004 ( Supplem...

Projection of Future Climate Change over Japan in Ensemble Simulations with a High-Resolution Regional Climate Model

“…The decreases or weakening of convection over the JPCZ were accounted for by the weakening of large-scale, low-level northwesterly winds associated with the winter monsoon. Mori et al (2014) concluded that cold winters driven by Arctic sea ice unlikely occur in the future climate, which is consistent with our results, although decreases in the ice may cause severe winter over central Eurasia in past decades.…”

Mechanisms influencing seasonal to inter-annual prediction skill of sea ice extent in the Arctic Ocean in MIROC

“…Meanwhile, SIC was assimilated at 1-day intervals following Lindsay and Zhang (2006) and Stark et al (2008). These assimilations were conducted over the period 1975-2011 with eight ensemble members produced by perturbing the sea surface temperature based on observational errors.…”

“…Although the exact cause is still being debated (e.g., Barnes and Screen, 2015), Mori et al (2014) have shown, using ensemble experiments with an atmospheric general circulation model, that the more frequent cold winters at midlatitudes can be partly explained by the sea ice decrease in the Barents and Kara Seas. Therefore, further investigation of the mechanisms driving Arctic sea ice variability is of great importance for more accurate projections of climate change, not only in the Arctic but also for the midlatitudes.…”

Robustness of the Warm Arctic/Cold Eurasian Signature within a Large Ensemble Model Experiment

“…To do this, we fi rst establish a reference EOF loading pattern based on the JRA-55 dataset. Region selected is 0°E−150°E, 40°N−90°N, slightly different from the defi nition used in Mori et al (2014). Next, for each ensemble run of both HPB and HPB-NAT experiments, we perform the same EOF analysis.…”

“…Mori et al (2014) showed through 100-member ensemble simulation of an atmospheric general circulation model (AGCM) that the second empirical orthogonal function (EOF) pattern reflecting such Arctic warming and mid-latitude cooling is robust and is approximately independent of the Arctic Oscillation (AO) signature. The pattern is named Warm Arctic/Cold Eurasian (WACE) and will be used to designate the pattern throughout this study.…”